Alloy steels



Patented Dec. 28, 1937 UNITED STATES ALLOY STEELS William MacCormac Burden,

and Reginald Harrison, Woolwich, England, assignors to Sofal Limited,

England No Drawing.

rial No. 117,092. 1935 4 Claims.

This invention relates to alloy steels.

The object .of the present invention is to produce an improved steel having an extremely high surface hardness value such as is particularly suitable for, example for articles intended to resist wear.

nitrogenized steels at present available are limited in their commercial utility by the fact that such processes require to be lengthy in order to produce any appreciable thickness of hardened surface layer and it has hitherto only been possible to produce either a very thin layer of high hardness or a moderately. thick layer of relatively low hardness.

The method of producing the steels forming the subject of the present invention however permits the nitrogenization process to be carried out with much more rapidity and results in the formation of a hard layer of greatly increased thickness.

The invention consists in the method of producing an alloy steeel having a high surface hardness value which comprises incorporating a proportion of tantalum or niobium with a steel of nil or low active carbon content and thereafter subjecting the same to a nitrogenization treatment in any suitable or known manner.

Normally in accordance with the invention the proportion of tantalum or niobium is in excess of that required to combine with any carbon in the steel.

Thus in accordance with the invention the tantalum or niobium may be employed in a proportion of up to for instance a proportion of from 2 to 6%.

Steels containing tantalum and niobium are known, these metals being incorporated in the steel for the purpose of increasing its toughness and susceptibility of hardening by heat treatment. It has never, however, been proposed to subject such steels to hardening by nitrogenization, and it is not known that they are capable of being so hardened very much more rapidly than the steels hitherto subjected to nitrogenization. It has been suggested that niobium or tantalum will combine with any nitrogen present in the metal bath during the formation of the alloy, thus purifying the bath. This, however, does not in any way indicate that the resulting steel will be suitable for nitrogenization, and still less that a hardened layer of given depth will be formed far more rapidly than has hitherto ever been observed.

Preferably the alloy steel in which the tantalum or niobium is incorporated is a low carbon steel containing the usual addition of a small pro- The known processes for the production of Reginald Genders, London, London,

Application December 21, 1936, Se-

In Great Britain April 30,

portion of'aluminium for instance of a proportion of 1%.

In one convenient manner of carrying the invention into effect a low carbon alloy steel of carbon content as low as possible (below .2%) and containing other elements as deired to give suitable properties vto the alloy is employed and an addition of tantalum or niobium is made'in the proportion of from 2 to 6% together with an addition of a small quantity of aluminium. The alloy so produced is then subjected to a nitrogenization treatment in dissociated ammonia at a temperature of 500-700" C. The surface hardened steel so produced has been found to give a hardness value of approximately 1,000 Vickers diamond hardness at a distance of 0.35 mm. from the surface when nitrogenized'at 550 C. for 24 hours, these properties being markedly superior to those of any previously known nitrogenized steel for which at least 50 hours treatment has been required to produce a hardened layer of appreciable thickness.

What we claim as our invention and desire to secure by Letters'Patent is:-

1. An article hardened in it marginal layers by nitrogenization, the article being made from an alloy consisting of iron, and containing carbon not substantially in excess of .2% and a proportion not exceeding 10% of at least one of the metals of the group consisting of tantalum, niobium in excess of any combined with carbon.

2. An article hardened in its marginal layers by nitrogenization, the article being made from an alloy consistingof iron, and containing carbon not substantially in excess of .2% and'from 2 to 6% of at least one of the metals of the group consisting of tantalum, niobium in excess of any combined with carbon.

3. An article hardened in its marginal layers by nitrogenization, the article being made from an alloy consisting ofiion and containing carbon not substantially in excess\, of 2%, a proportion not exceeding 1% of aluminum and a proportion not exceeding 10% of at least one of the metals of the group consisting of tantalum, niobium in excess of any combined with carbon.

4. An article hardened in its marginal layers by nitrogenization, the article being made from an alloy consisting of iron, and containing carbon not substantially in excess of 2%, a proportion not exceeding 1% of aluminum and from 2 to 6% of at least one of -the metals of the group consisting of tantalum, niobium in excess of any combined with carbon.

WILLIAM MACCORMAC BURDEN. REGINALD GENDERS. REGINALD HARRISON. 

